In modern society, elevators have become ubiquitous machines for transporting people and cargo through buildings of multiple stories. As elevators are operated continually throughout the day making frequent stops at various floor levels, the braking system of an elevator plays an important role in the smooth operation of the elevator.
Gearless machines such as elevators or other belt-driven systems typically employ a mechanical or electromechanical braking system to stop or temporarily hold a particular motion. Electromechanical brakes of elevators, for instance, generally employ a clutch-type braking mechanism for supplying a holding or braking torque that is sufficient for slowing or holding an elevator car at a fixed position. The braking torque supplied by clutch-type brakes is mechanically produced by the friction that is generated between a rotating brake disk that is rigidly attached to a machine shaft and a set of friction pads that is releasably placed in contact with a surface of the brake disk. The engagement or disengagement of the friction pads is electromechanically controlled by a brake coil. Moreover, when the brake coil is activated, a magnetic attraction between the armature plates and an electromagnetic core causes the friction pads to disengage from the surface of the brake disk. When the brake coil is deactivated, springs that engage the armature plates urge the armature plates into engagement with the surface of the brake disk. Although such clutch-type brakes have been proven to be effective and are still widely used today in various gearless applications such as elevators, and the like, they still have room for improvement.
For instance, the range of braking torque that a specific clutch-type brake can variably apply is relatively narrow. For example, a clutch-type brake cannot provide a different stopping power in certain situations (e.g. emergency stops, or the like) than in other situations (e.g. normal stops, or the like). During an emergency, such as loss of power to the building, an elevator must be able to perform an emergency stop. An emergency stop can be abrupt, causing the elevator car to jerk, which can be an uncomfortable experience for passengers traveling within the elevator car. Emergency stops also wear down the braking system. Furthermore, the braking system installed to handle such emergency stops must be bulky and expensive.
Conversely, a clutch-type brake cannot provide reduced stopping power for normal stops than with emergency stops. A typical clutch-type brake is limited to its rated torque which is further dictated by the invariable mechanical limits of the brake, material composition of its friction pads, and the like. Therefore, in normal operation, an elevator equipped with a bulky heavy duty braking system will provide the same braking torque for a normal stop than it would with an emergency stop. Thus, the elevator car, as well as the passengers within it, may experience a jerk every time the braking system is engaged to stop the elevator. Accordingly, it follows that clutch-type brakes do not offer control or variation of the braking torque.
In light of the foregoing, improvements continue to be sought for smoothly stopping an elevator with minimal strain on the system.